There is a need with many manufacturing operations and processes and within liquid transportation systems to monitor the composition or other properties of the liquid material which is either contained in or flowing within a vessel. Often what is required is to capture a sample of the liquid from within the vessel in order to make the necessary measurements. It is most desirable to be able to capture such samples without interference with or contamination to the processes being monitored. Non-interference with a process is often achieved by ensuring that vessel pressure is maintained throughout the sampling-capturing operation. Further, it is often a requirement that samples be taken at regular and frequent intervals so that reliability, operator safety, and sampler maintenance and longevity are important requirements for such samplers.
A number of samplers which are used in such manufacturing or process applications are devices which capture small, discrete samples of liquid. An example of such a sampler is disclosed in U.S. Pat. No. 6,792,818 by Ben E. Jaeger. This positive-displacement sampler includes a plunger having a sample receiving recess and a connecting device which couples the sampler to a vessel at an aperture in the vessel. The sampler is attached to the connecting device, and the connecting device is moveable between a first position placing the sampler into, and a second position taking the sampler out of communication with the aperture. With the connecting device in the first position, the plunger is reciprocated to extend the plunger and its recess through the connecting device and vessel aperture into product in the vessel to receive a product sample in the recess. The plunger is then retracted from the vessel and through the connecting device to deliver the product sample to a collection point. During reciprocation of the plunger, a liquid seal is maintained between the vessel interior and sample collection point, and when the connecting device is moved to the second position, the sampler can be detached from the connecting device for service or repair, without escape of liquid from the vessel through the connecting device.
Particularly severe requirements exist for samplers used in applications where the liquid being sampled contains a solid phase. An example of this is in the handling of oil sands in which the liquid may contain bituminous sand, oil, hot water, and possibly clay. The solid phase is the source of abrasive material which creates a particularly difficult operational environment for samplers. The abrasive material can become trapped in regions around seals, particularly when elements within the sampler become misaligned due to, for example, frictional forces during movement of sampler elements, thereby allowing the abrasive material to flow by leakage into areas in which it is not intended to be, causing excessive wear. Also, when seals move past entry and exit interfaces within valves and other elements within a sampler, abrasive material can easily cause the seals to wear far too rapidly, necessitating frequent and costly maintenance on the sampler.
The sampler disclosed in U.S. Pat. No. 6,792,818 described above, when applied in applications such as oil sands, operates in a manner in which excessive seal/interface traverses and misalignment are both causes of seal wear. As an example, in the sampling of such abrasive liquids, sampling frequencies may be as high as five samples per hour and may result in seals being replaced as often as once each week, creating an extremely high maintenance cost.
Another desirable and intended feature for samplers is the ability to be able to achieve what is termed “double block and bleed” capability, the ability to isolate the sampler from vessel pressure and to verify that such isolation has indeed taken place so that the sampler can be disconnected. If seals are worn and misalignment causes further leakage, the sampler cannot be relied on to achieve the required isolation. The invention disclosed in the '818 patent can exhibit such unwanted behavior when the ball valve, which is “floating” within a set of seals, becomes misaligned and causes leakage of unwanted vessel pressure, thereby causing a potentially unsafe condition for an operator performing maintenance on the sampler or simply taking a sample in the course of regular vessel monitoring.
U.S. Pat. No. 5,905,213, also by Ben E. Jaeger, discloses a sampler in which the forward end of the sampler housing is coupled to a movable valve for movement with the valve, and the housing and valve have axially-aligned bores. Movement of the valve places the forward end of its bore into and out of communication with an opening in a vessel containing the liquid to be sampled. A plunger in the housing bore has a sample-receiving recess intermediate its ends, and with the forward end of the valve bore placed into communication with the interior of the vessel, the plunger is reciprocated forward in the housing and valve bores to project the recess into the vessel to receive a product sample therein. The plunger is then reciprocated rearward to retract the product sample containing recess from the vessel and through the valve and housing bores to a sample collection point in the housing. When repair or replacement of the sampler is required, the valve is moved to place the forward end of the valve bore out of communication with the vessel interior, whereupon the sampler housing can be disconnected from the valve without outflow of liquid product from the vessel through the valve bore. A disadvantage of the arrangement is that the entirety of the sampler moves conjointly with movement of the valve between its open and closed positions, so a relatively large unobstructed area must be provided around the sampler to accommodate such movement, which limits freedom of location of the sampling apparatus. In addition, to accommodate mounting of the sampler housing on the valve, the valve must be relatively large to accommodate connection of the sampler housing to it, resulting in increased manufacturing costs.
Existing samplers currently used as described above fall short of delivering effective, safe and cost-effective sampling. Thus, there is a need for a sampler which satisfies the objectives as set forth in the following section.